Rectifying apparatus



Oct. 23, 1951 w. H. BIXBY RECTIF'YING APPARATUS Filed Oct. 19, 1948 5?FIG.

OFF

70 SOURCE 2/ WVENTOR W H. B/XBY ATTORNEY Patented Oct. 23, 1951RECTIFYING APPARATUS William H. Bixby, Detroit, Mich., assignor toDonald R. Middleton and Stanley M. Hanley, doing business as PowerEquipment Company, Detroit, Mich., a copartnership Application October19, 1948, Serial No. 55,340

8 Claims.

This invention relates to rectifying apparatus and particularly to arectifier comprising two grid-controlled gaseous discharge devicesoperating in parallel.

The principal object of the invention is to provide means for initiatingconduction at effectively the same instant in two grid-controlledgaseous discharge devices operating in parallel.

A further object of the invention is to provide a new andimproved'control system for two gridcontrolled gaseous discharge devicesoperating in parallel whereby the currents in the two devices,

respectively, are maintained substantially equal.

A characteristic of a grid-controlled gaseous discharge tube is that, inorder to start conduction between the anode and cathode, it is necessaryto first form an arc discharge between the control grid and the cathode.The grid voltage required for this depends upon the anode voltage andupon the design of the tube. When conduction starts, the grid thereafterloses control until the flow of current between anode and cathode isinterrupted, after which it regains control until another breakdownoccurs between grid and cathode.

For the successful operation of two such tubes in parallel, for greaterrectified output, it is desirable that the tubes become conducting atpractically the same instant in the cycle of the supply voltage, andthat during the conducting portion of the cycle the current remainsubstantially equal in two tubes. Assuming the first condition to besatisfied, the latter requirement can be met by means of a center-tappedequalizer coil with one-half of its winding connected in series with oneof the tubes and the other half in series with the other tube. Sinceconsiderable variation in the critical grid firing voltage is commonbetween tubes of the same type, it is preferable that the voltageapplied to the grids of the tubes have a very steep wave front in orderto raise the gridcathode voltages of the two tubes, respectively, abovethe critical firing voltage at the same time. If a circuit for producingan abruptly rising peaking voltage were used for this purpose, the loadcapacity of the circuit would. of course, need to.

the other tube, that is, the controlling tube, there is impressed afiring voltage which need not be peaked but which may be a voltageobtained from an alternating-current supply source. When the controllingtube is fired and space current begins to flow therein, a voltage isthereby induced in the auxiliary winding which immediately fires thecontrolled tube. Throughout the rest of the cycle the current ismaintained equally divided between the tubes by the well-known action ofthe equalizer coil.

Under certain circumstances, as hereinafter explained, the auxiliarycoil may be dispensed with and the above results obtained by means ofthe equalizer coil.

The invention is applicable to the operation of two grid-controlledgaseous discharge tubes connected in parallel as a half-wave rectifier,or two pairs of such tubes connected as a full-wave rectifier.

The invention will be more clearly understood from the followingdetailed description and the accompanying drawing, of which:

Fig. 1 is a schematic view of a half-wave rectifier embodying theinvention;

Fig. 2 is a modification of the circuit of Fig. 1; and

Fig. 3 is a schematic view of a full-wave rectifier embodying theinvention.

Referring to Fig. l, the grid-controlled gaseous discharge tubes I and 2are connected in parallel to form a half-wave rectifier for supplyingrectified current from an alternating-current source 3 to a load 4. Theprimary of a transformer 5 is connected to the alternating-currentsource 3 and its secondary is connected between one side of the load 4and the midpoint of an equalizer coil 6. The end terminals of theequalizer coil are connected respectively to the anodes of tubes l and2. The cathodes of the tubes are connected in parallel across thecenter-tapped secondary l of a heater transformer, the primary of whichis omitted from the drawing. The midpoint of the secondary l isconnected to the other side of the load 4.

The grids of tubes l and 2 are provided with a negative bias from apotentiometer 8 connected in parallel with a condenser 9 across theoutput terminals of a bridge rectifier ID, to which alterhating currentis supplied from source 3. A firing voltage for tube l is supplied by atransformer H, the primary of which is connected to source 3 and thesecondary of which is connected between the grid and cathode of thistube in series with a portion of the biasing potentiometer 8 winding I3is, in eifect, a transformer having a center-tapped primary.

When at the beginning of a half cycle of the the source 3, the secondaryof transformer :5 is applying an increasing positive voltage to theanodes of tubes l and 2, at the .same time the secondary of transformerI! is applying a .posi-' tive voltage to the grid of tube 1. When thelatter voltage has sufliciently overcome the negative bias provided byrectifier l9, tube ionizes and becomes conducting its grid-cathodecurrent being limited byresistor l2. Current then flows ,through theupper ,half of the equalizer coil through the-anode cathode space oftube 1, and through the load I! back to the secondary .of

transformer-5. The initiationof current through .theupper half vof coil3 induces ahigh voltage .in .the auxiliary winding is which is applied.to the grid of ,tube 2. The auxiliary winding is .so designed that thisinduced YOltage is great .enough to assure the firing of tube ,2,excessive gridcathode current being prevented by resistor i l. Currentwill then how through the lower half [of the equalizer coil .3, throughthe anode-cathode space of tube 2, and through the load 4 back to thesecondary of transformer 5. Thus conduction is started in tube ,2 atpractically the same instant that conduction is initiated in tube I.Thereafter, during the remainder of the cycle of the a t a in urrent s uce. the curr nt will divide equally between the two tubes, or nearly so,,due to the balancing action of the equalizer .coil For instance, if thecurrent in tube .I should tend to increase more rapidly than the currentin tube 2,.therchoking action of .the upper half of the coil 6 wouldtend to retard the in-- crease in tube I, while at the same time avoltage would be induced in the lower half of coil 6 which would tend toincrease the current through tube 2. In this manner the reciprocalaction tends to maintain the two currents approximately equal.

:Inthe operation .of the above circuit it is necessary to adjust thenegative bias provided by pctentiometer 55 to a value that will alwaysprevent the firing pf tube 2 until the start .of current tube I.

In Fig, 2 there is shown a modification of the circuitof Fig. 1 whereinthe equalizer coil is connected on the cathode side of the tubes insteadof on the anode side. Like characters are used to designate the sameelements in these figures. As in Fig. 1, alternating-current source 3,supplies-power to transformer 5, one end of the secondary beingconnected to one side of the load 4 and the other end to the anodes oftubes I and 2. In this case the cathodes are separately heated by thecenter-tapped secondary windings I5 and IE of a heater transformer, theprimary of which is not shown. The midpoint of secondary 1315 connectedto one terminal of the equalizer coil 6 and the midpoint of secondary i6is conof a load 29..

4 is supplied by transformer ll. Switch I! in one position connects coill3 in the grid-cathode circuit of tube 2 and in the other position itexcludes the coil.

With switch I! in the down position as shown. this circuit operates inthe same manner as that of Fig. lghut has an advantage over th'e former.in the following respect. When, in Fig. 2, current begins to flowthrough tube l and through the upper half of equalizer coil 6, a voltageis thereby induced in the lower half of the coil whichmakes the cathodeof tube 2 more negative with respect to its grid. This voltage thereforeaidsin :thefiring-of tube 2. If its magnitude were great enough theauxiliary winding could be omitted entirely. This may be accomplished byoperating switch H to the up position, the grid of tube '2 then beingconnected directly to the negative terminal of the bias supply.

Fig. 3 illustrates an :application of the invention to a full-waverectifier, in which two tubes .of va typesuch as shown in Figs. 1 and;:2 .are op.- erated in parallel to .rectifyone Ihalf of the wave and asimilar pair of tubes to rectify the ether half. In this figure tubes.24 and .25 are connected :as a full-wave rectifier to supply directcurrent -to a load 29, .and would ,so operate with tubes 24' and 25'removed .from their sockets. With the two latter tubes in position,however, the .fir'ing. of tube .24 on one .half cycle causes tube 2 3 tofire, these two tubes sharing the load current in parallel. When tube .2.5 begins to ccnduct, on the next half cycle it causes tube 25' to con.-duct "and these two tubes divide the .lcadrduring this half cycle. Tubes25 and25 act theref qre as controlling tubes, while tubes :24 and 25'are the controlled tubes.

- Referring first to the .upper half of-Eig'the primary winding oftransformer .20 is connected to the alternatin -current source 21. Thesec ,ondary is divided into two parts, winding and winding 23. The upperterminal cf-winding 2.21s connected to the anode of tube 2-4 and thelower terminal of winding 23 to the-anode of tube 25.

; The other terminals of the two secondarywindin s are joined togetherthrough the upper .half

of an equalizer coil 23, .a conduct-or 27., and the lower half of anequalizer coil 1-26". Conductor :2 is connected through a choke coil "28to one side The cathodes of tubes 24 and 25 are connected in parallelacross :the center-tapped secondary 39 of a heating transformer, theprimary of which is not shown, and the center tap is connected to theother side of the loa'd29. A condenser 31 is connected across the outputterminals of the rectifier, forming a smoothing filter in combinationwith-choke coil 28. The grids of tubes Hand 25 are connectedrespectively to the terminals of .the center-tapped secondaryof atransformer 32, the midpoint of the transformer winding being returnedthrough switch 33 to the cathodes via the center tap-of the secondarywinding Current limiting resistors 34 and 35 are connected respectivelyin the grid-cathode circuits of tubes 24 and 25".

Potentiometer 36 in series with resistor 31, which is shunted by avoltage regulating gas tube 38 and a condenser 39, are connected acrossthe output terminals of the rectifier. Potentiometers .40 and 4| andcondenser-A2 are connected in par.- allel across the output terminalsof. an auxiliary bridge rectifier 43, which is supplied with alteratingcurrent from source 2|. When switch 33 is in the on position it connectsthe midpoint .of the secondary of transformer .32 to the slider ofpotentiometer 36, and when in the off position to the slider ofpotentiometer 4 I.

It will be seen that the portion of Fig. 3 just described constitutes anordinary full-wave rectifier, employing a single grid-controlled gaseousdischarge tube for each half cycle of the alternating current to berectified. In the lower half of the figure, with exceptions to be noted,tubes 24 and 25 are connected as a similar full-wave rectifier, with itsoutput terminals in parallel with'those of the first rectifier. Forconvenience, the corresponding elements in this half of the drawing aregiven the same reference numbers asthose in the upper half, but with theaddition of primes to distinguish them. Here the lower terminal ofsecondary winding 22' is joined to the upper terminal of windin 23through the lower half of equalizer coil 26, conductor 21, and the upperhalf of coil 26. The grid of tube 24 is connected to' one end of theauxiliary winding 44, which is in inductive relation to equalizer coil25, and similarly the grid of tube 25' is connected to one end of theauxiliary winding 44', which is in inductive relation to coil 26'. Theother terminals of the auxiliary windings 44 and 44 are connectedtogether and to the slider of potentiometer 40. The cathodes of tubes 24and 25 are connected in parallel with those of,

tubes 24 and 25.

For the protection of gaseous rectifier tubes of this kind it isgenerally desirable to delay" conduction after the application of anodevoltage until the cathodes have become heated to transformer 20, andwith the slider of potentiometer 40 likewise adjusted for non-operationof tubes 24 and 25'. When the switch is turned to the on position afterthe warm-up period, tube 24 will fire near the start of a half cycle ofpositive voltage on its anode and grid, and current will begin to fiowthrough its anode-cathode space, through the load 29, through the upperhalf of equalizer coil 26, and thence back to the secondary winding 22.The voltage thereby induced in the auxiliary winding 44 will cause tube24 to begin conducting also, the path of this current bein fromsecondary winding 22' through the anode-cathode space of the tube,through the load 29, through the lower half of equalizer coil 26, andthence back to the secondary, and through the rest of the half cycletubes 24 and 24' will operate in parallel and share the load equallythrough the action of equalizer coil 25; as previously explained forFigs. 1 and 2.

In the same manner, near the beginning of the next half cycle thecontrolling tube 25 will start conducting and current will flow throughits anode-cathode, space, through the load 23, through the lower half ofequalizer coil 26', and thence back to the secondary winding 23. Thevoltage thereby induced in the auxiliary winding 44 will cause tube 25to fire immediately afterwards, and current will start flowing throughits anode-cathode space, through the load 2?, through conductor 21, andthrough the u per winding 23'.

half of equalizer coil 26' back to the secondary Equalizer coil 26 willthen act to maintain equality of the currents in tubes 25 and 25'through the rest of this half cycle, in the manner previously explained.

In the adjustment of the biasing potentiometer 36 it is necessary tomake sure that the negative bias is suflicient to prevent eithercontrolled tube from firing ahead of its controlling tube. This biaswill then be satisfactory for the warmup period also, i. e., with switch33 in the "01! position.

When the circuit is operating with switch 33 in the on position, thenegative bias for the controllin tubes 24 and 25 provided bypotentiometer 36 fluctuates with the output voltage, thus varying theinstant of firing. This exercises a regulating effect on the voltage,tending to keep it constant. The purpose of the constant voltagedischarge tube 38 connected across .resistor 31 is to concentrate theentire variation in output voltage across potentiometer 35. I In Figs. 1and 2, for simplicity, the provision of a separate biasing voltage forthe warm-up period is omitted, and likewise the voltage regulatingfeature just mentioned.

What is claimed is:

1. In combination, a first and a second gaseous discharge device eachhaving an anode, a cathode and a control electrode, a center-tappedreactance coil, means for supplying current from an alternating-currentsupply source to a load through a circuit having two parallel branchpaths, each including the space current path of one of said devices inseries with one half of said reactance coil, an auxiliary coil ininductive relation to said react-ance coil, a circuit including saidauxiliary coil connecting the control electrode and cathode of saidsecond device, and means for impressing upon the control electrode ofsaid first device a potential with respect to its cathode for causingthe control of space currentin both of said devices.

2. In combination with a rectifier comprising a first and second gaseousdischarge device, each having an anode, a cathode and a controlelectrode, said devices being connected in parallel paths which are inseries with an alternatingcurrent source and a load, a control systemfor insuring substantially equal division of current in said devicescomprising a center-tapped equalizer coil the two halves of which areconnected respectively in series with the anode-cathode discharge pathsof said devices, an auxiliary coil in inductive relation to saidequalizer coil, a circuit including said auxiliary coil connecting thecontrol electrode and cathode of said second device, and means forimpressing upon the control electrode of said first device a potentialwith respect to its cathode for initiating conduction therein andthereby initiating conduction immediately afterwards in said seconddevice.

3. In a rectifying circuit having two parallel branch paths throughwhich currents are transmitted from an alternating-current source to aload, said paths respectively comprising a first and a second gaseousspace current rectifying device each having an anode, a cathode and acontrol electrode, means for controlling the current supplied from saidsource to said load comprising an inductance device having a first and asecond winding, means for connecting respectively different portions ofsaid first winding in the said parallel branch paths, a circuitconnecting the control electrode and cathode of said r secondrectifyingdevice including said second rvinding, and a circuit connecting thecontrol electrode and cathode of said first rectifying device includinga source of voltage for causing conduction to be initiated in said firstdevice and "thereby causing the initiation .of conduction in said seconddevice. Y

, ,4. In a rectifying circuit having two parallel branch paths throughwhich currents are transmitted from an alternating-current source to aload, said paths respectively comprising a first and a second gaseousspace current rectifying device each having an anode, a cathode and acontrol electrode, means for insuring substantially equal division ofcurrent in said rectifying 1 devices comprising an inductance devicehaving afirst :and a second winding, means for connecting1differentportions of said first winding respectively between the anodes of saidrectifying devices and the said alternating-current source, .a' sourceof directacurrent biasing voltage, a circuit connecting the controlelectrode and cathodeof said second rectifying device including saidsecond winding and said source of biasing voltage: and a circuitconnecting the control electrode and cathode of said first rectifyingdevice including said source of biasing voltage and a source of voltagefor causing conduction to be initiated in said first device and therebycausing the initiation of conduction in said second device. 1 5! In arectifying circuit having two parallel branch paths through whichcurrents are transmitted from an alternating-current source to a load,said paths respectively comprising a first land a second gaseous spacecurrent rectifying device. each having an anode, a cathode and a controlelectrode, means for insuring substantially equal division of current insaid rectifying devices comprising an inductance device having a firstand a second winding, means for connecting a first portion of said firstwinding between the cathode of said first rectifying device and saidload and a second portion of said first windins between the cathode ofsaid second rectifying ,device and said load, a source of direct-currentbiasing voltage, a circuit connecting the control electrode and cathodeof saidsecond rectifying device including in series said second windinc.said source of biasing voltage and said secend portion of said firstWinding, and a circuit connecting the control electrode and cathode ofsaidfirst rectifying device including in series said source of biasingvoltage, said first portion of said first .winding and a sourceofvoltage for causing conduction to beinitiated in said first deviceandthereby causing the initiation of conduction in said second device.

6. in a rectifying circuit having two parallel branch paths throughwhich currents are trans-,- -rnitted from an alternating-current sourceto a load,- said paths'respectively comprising a first and a secondgaseous space current rectifying device each having an anode, a cathodeand a control electrode, means for insuring substantially equal divisionof current in said rectifying devices comprising a center-tappedinductance coil, means for connecting one half of said coil between thecathode of saidfirst rectifying device and the said load and the secondhalf of said 8 coil between the cathode of said second rectifying deviceand the said load, a source of direct- .current biasing voltage, acircuit connecting the control electrode and cathode of said second rece,tifying device including said source of biasing voltage and said secondhalf of said coil, and a circuit connecting the control grid and cathodeof said first rectifying device including the first half of said coil,the said source of biasing-voltage and a source of voltage for causingconduction to be initiated in said first device and thereby causing theinitiation of conduction in said second device. 1

'1. In a rectifying circuit having two parallel branch paths throughwhich currents are trans-v mitted from an alternating-current sourceto-a load, said paths respectively comprising a first and a secondgaseous space current rectifying device each having an anode, a cathodeand a control electrode, means for insuring substantially equal divisionof current in said rectifying devices comprising an inductance devicehaving a center-tapped first winding and a second Wind ing, means forconnecting the two halves ofsaid first winding respectively in the saidparallel branch paths, a source of direct-current biasing voltage, acircuit connecting the control electrode and cathode. of said secondrectifying device in cluding said source of biasing voltage and saidsecond winding, and a circuit connecting thereontrol electrode andcathode of said first rectifying device including said source of biasingvoltage and a source of voltage for causing conduction to be initiatedin said first device and thereby causingthe initiation of conduction insaid sec-v ond device.

8. In combination, a first and a second gaseous space current deviceeach having an anode, a cathode and a control electrode, means for sup?plying current from an alternatingecurrent source to a load through acircuit having two parallel branch paths, an inductance device having afirst and a second winding, means for connecting said windings in saidbranch paths respectively between a first terminal of said load and saidcathe odes respectively, control circuits including said windingsrespectively for connecting the control electrode and cathode .of saidspace current de vices respectively, and means for impressing analternating voltage upon one only of said control circuits tocauseconduction to be initiated repeatedly and substantially simultaneouslyin both said space current devices.

WILLIAM H. BIXBY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,995,810 Klemperer Mar. 26, 19352,088,474 Haller July 27, 1937 2,134,530 Philpott et a1 Oct. 25, 1938 VFOREIGN PATENTS Number Country Date 445i1 8 Great Britain Apr. 2, 1936

